WARNING: This page is about a different car, the 2004 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
Measure the speedometer resistance.
Fig 1: Measuring Speedometer Resistance
Courtesy of SUBARU OF AMERICA, INC.
Fig 2: Speedometer Resistance Table
Courtesy of SUBARU OF AMERICA, INC.
If NG, replace the speedometer.
If OK, replace the combination meter printed circuit.